Laboratory Studies
- Generally, laboratory studies are not required for a routine assessment.
- However, if systemic or metabolic disease is suspected, the following studies can be of value in determining etiology or disease activity:
- Uric acid
- Sedimentation rate
- C-reactive protein
- Antinuclear antibody (ANA)
- Rheumatoid factor
Imaging Studies
- Radiographic views: Radiography continues to be the standard means with which to assess joint pathology and measure angular deformity. Weightbearing anteroposterior (AP), lateral oblique (LO), lateral (LAT) projections, and sesamoid axial view should be obtained in the angle and base of gait (see images below). Non–weightbearing radiographs may reveal the osseous relationships differently, causing an improper selection of surgical procedure. Weightbearing radiographs demonstrate the structural status of the foot.
Anteroposterior and lateral radiographs, weight-bearing views. 
The medial bony enlargement is more prominent on this lateral oblique projection than on other views. - The AP projection is used to determine the intermetatarsal angle, metatarsus adductus angle, hallux abductus angle, proximal articular set angle, and hallux abductus interphalangeus, as well as the first metatarsal length, sesamoid position, first metatarsophalangeal joint condition, bone stock, first metatarsal base, hallux rotation, and medial metatarsal head enlargement (see images below).
Template showing angular measurements. 
Another template showing increase angular relationships. - The LAT projection is used to determine first metatarsal sagittal plane position and dorsal exostosis and/or osteophytes.
- The LO projection is useful in evaluating bone stock and presence of dorsomedial exostosis. Because the bunion is located on the dorsomedial aspect of the metatarsal head, the prominence may be appreciated fully only in an oblique view.
- In the sesamoid axial view, the sesamoids are observed for any lateral subluxation out of their respective grooves. As well, the crista is evaluated for erosion created by this subluxation. The joint sesamoid-metatarsal joint space is also examined for degenerative changes.
- The AP projection is used to determine the intermetatarsal angle, metatarsus adductus angle, hallux abductus angle, proximal articular set angle, and hallux abductus interphalangeus, as well as the first metatarsal length, sesamoid position, first metatarsophalangeal joint condition, bone stock, first metatarsal base, hallux rotation, and medial metatarsal head enlargement (see images below).
- Radiographic angular relationships: various angles, structures, and positions are assessed as listed below.
- Intermetatarsal angle: Normal is 8-12° in a rectus foot and 8-10° in an adductus foot type. This angle is the relationship between the longitudinal axis of the first and second metatarsal. If the angle is increased, the condition is termed metatarsus primus adductus.
- Metatarsus adductus: Normal is less than 15°; more than 15° is considered adductus. This angle is the relationship between the longitudinal axis of the lesser tarsus and the second metatarsal. This angle indicates whether the forefoot is in a rectus or adducted attitude in reference to the rearfoot. The rectus foot has a metatarsus adductus angle less than 15°. An angle larger than 15° causes the hallux valgus deformity to appear more severe than it actually is.
- Hallux abductus angle: The normal upper limit is 15-20°. This angle is the abduction of the longitudinal bisection of the proximal phalanx and first metatarsal; it is also known as the first metatarsal phalangeal angle. This is the primary method for quantification of the hallux abductus, either positional or structural.
- Proximal articular set angle: The normal upper limit is 7.5°. This is a measurement of the structural position of the first metatarsal head cartilage. It is used in determining whether the joint is congruent, deviated, or subluxated (see image below).
Congruency of the first metatarsophalangeal joint. - Distal articular set angle: The upper limit of normal is 7.5°. This angle detects structural abnormalities of the proximal phalanx base. Abnormalities may indicate the need for proximal phalanx osteotomies. The angle is determined by longitudinal bisection of the proximal phalanx of the hallux with reference to a line that connects the medial and lateral extents of the proximal phalangeal articular surface. The degree of abduction of the phalangeal bisection away from 90° determines this angle.[3]
- Sesamoid position: Positions 1-3 are normal, and the range is 1-7 (see image below). In pathologic hallux valgus, the crista often is eroded as a result of the laterally deviated position of the sesamoids. The sesamoid position represents the degree of lateral subluxation of the sesamoid apparatus.
Tibial sesamoid position with bisection of the first metatarsal. Positions 1-3 are normal. Positions 4-7 indicate erosion of the crista and a laterally track-bound, nonreducible hallux valgus. - First metatarsal declination angle: Ranges from 15-30° are normal. This angle is determined by bisection of the first metatarsal shaft in reference to the weightbearing surface. This is a useful evaluation for selection of a procedure that includes plantarflexion of the metatarsal in the sagittal plane.
- Hallux valgus interphalangeus angle: The upper limit of normal is 10°. A measurement larger than this indicates a structural deformity of either the proximal phalanx head or the distal phalanx base. This causes the hallux to have an abducted appearance, which occasionally is confused with a hallux valgus deformity. An inability to detect an abnormal angle may lead the surgeon to overcorrect a hallux abductus. The angle of abduction is determined on an AP view from longitudinal bisection of the proximal phalanx compared with longitudinal bisection of the distal phalanx.
- Radiologic pathology: Radiographs may be useful in evaluating the condition of the first metatarsophalangeal joint. A couple aspects should be evaluated.
- The first aspect is the width and uniformity of the joint space (see images below). Normally, the joint space appears uniform. An increase or irregularity is indicative of degenerative changes. Therefore, if the osteoarthritis is severe enough, a joint-destructive procedure should be entertained.
Bunion deformity with minimal joint destruction. 
Bunion deformity with significant joint destruction. - The joint should also be evaluated for osteophytes at the articular margins. The normal joint is free of osteophytes. Osteophytes are yet another indication of the severity of degeneration.
- The first aspect is the width and uniformity of the joint space (see images below). Normally, the joint space appears uniform. An increase or irregularity is indicative of degenerative changes. Therefore, if the osteoarthritis is severe enough, a joint-destructive procedure should be entertained.
- Radiographic bone stock: Radiography is an excellent method for determining the quality and density of bone.
- In general, bone density should be uniform and trabeculation should be fine.
- The head of the metatarsal should be evaluated for cysts. In the normal metatarsal head, cysts should not be observable. Cysts indicate structural adaptation of the bone to function and load, or systemic arthritis.
- Severe osteopenia or cysts may preclude the use of various forms of internal fixation or osteotomy. Note any increased density of the second metatarsal, which indicates excessive forces on the second metatarsal due to instability of the first metatarsal. Stress fractures of the second metatarsal commonly occur in this setting (see image below).
Large intermetatarsal angle and hallux abductovalgus deformity secondary to previous injury. Note the increased cortical density of the second, third, and fourth metatarsals.
- Other radiographic findings: Depictions of hallux valgus, the medial eminence, and the soft tissue are evaluated as well.
- Hallux valgus: No valgus rotation, as noted by the symmetrical concavity of the borders the medial and lateral shafts, should be evident. Asymmetry indicates the need for a procedure to the proximal phalanx to derotate the hallux.
- Medial eminence: The normal metatarsal head is free from excessive bony proliferation. Bony proliferation indicates an the imbalance of the joint with excessive medial tension.
- Soft tissue: The soft tissues are evaluated for edema, bursae, calcification, or other signs of chronic inflammation.
- Other imaging studies usually do not help in determining the degree of deformity or in evaluating the condition of the joint. However, one possible adjunct study is technetium 99m–labeled hydroxyapatite bone scanning to rule out osteomyelitis if ulceration is present and if the radiographic findings are inconclusive.
Staging
Root et al described the pathomechanical development of hallux valgus in 4 stages.[4]
- In stage 1, excessive pronation causes hypermobility of the first ray, causing the tibial sesamoid ligament to be stretched and the fibular sesamoid ligament to contract; lateral subluxation of the proximal phalanx occurs.
- In stage 2, hallux abduction progresses, with the flexor hallucis longus and flexor hallucis brevis gaining lateral mechanical advantage.
- In stage 3, further subluxation occurs at the first metatarsophalangeal joint, with formation of metatarsus primus adductus.
- In stage 4, the first metatarsophalangeal joint finally dislocates.
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